1. Field of the Invention
The present invention relates to low NO.sub.x formation burner apparatus and methods of burning fuel gas--air mixtures whereby flue gases having low NO.sub.x content are produced.
2. Description of the Prior Art
The environmental emission standards imposed by governmental authorities are continuously becoming more stringent. Such standards limit the quantities of gaseous pollutants such as oxides of nitrogen (NO.sub.x) and carbon monoxide which can be emitted into the atmosphere. As a result of the standards, improved burner designs have been developed which lower the production of NO.sub.x and other polluting gases. For example, methods and apparatus wherein fuel is burned in less than a stoichiometric concentration of oxygen to intentionally produce a reducing environment of CO and H.sub.2 have been proposed. This concept has been utilized in staged air burner apparatus wherein the fuel is burned in a deficiency of air in a first zone producing a reducing environment that suppresses NO.sub.x formation, and the remaining portion of air is introduced into a second zone.
Methods and apparatus have also been developed wherein all of the air and some of the fuel is burned in a first zone and the remaining fuel is burned in a second zone. In this staged fuel approach, an excess of air in the first zone acts as a diluent which lowers the temperature of the burning gases and thereby reduces the formation of NO.sub.x. Other methods and apparatus have been developed wherein flue gases are combined with fuel gas--air mixtures to dilute the mixtures and lower their combustion temperatures and the formation of NO.sub.x.
While the prior art methods and burner apparatus for producing flue gases having low NO.sub.x contents have achieved varying degrees of success, there still remains a need for improvement in gas burner apparatus and methods of burning fuel gas whereby simple economical burner apparatus is utilized and low NO.sub.x content flue gases are produced.